This sounds like an interesting item, and if it has an original Handel autograph, it is likely to be quite valuable. 'The Messiah' is an English-language oratorio composed in 1741. It isn't the name of a painting, or at least, not one by George Frederich Handel. I would strongly advise you to have this item looked at by an art sales professional, preferably at a good quality auction house. Email in the first instance including photographs and a full description.
It is impossible to value any artwork accurately without seeing it in person, and this is especially true of the kind of unique item that you potentially might have.